Application domain — when to use an impulse turbine Select the head range for which impulse turbines (e.g., Pelton) are generally preferred in hydroelectric installations.

Introduction:
Hydraulic turbine selection depends primarily on available head and discharge. Impulse turbines like the Pelton convert pressure head entirely to jet velocity before striking the runner, making them ideal where head is high and discharge is relatively low.

Given Data / Assumptions:

• High elevation drop (tens to hundreds of meters).
• Relatively low flow rates compared to low-head sites.
• Stable water supply or controllable nozzles to modulate power.

Concept / Approach:
At high heads, nozzle velocities become large (v ≈ sqrt(2gH)), enabling efficient energy transfer by impulse action. Reaction turbines (Francis, Kaplan) are typically preferred for medium and low heads, respectively, to keep runner sizes practical and maintain efficiency.

Step-by-Step Solution:

Verification / Alternative check:
Design manuals and selection charts consistently place Pelton at high head–low discharge corner of the selection map.

Why Other Options Are Wrong:

• Low/medium head: usually reaction machines are better suited.
• High discharge (as an option alone): discharge magnitude alone does not define the type; high Q with low H favors Kaplan/propeller.
• Ultra-low head: specialized low-head turbines are used.

Common Pitfalls:
Assuming turbine type depends only on discharge; ignoring cavitation constraints and runner diameter practicality at given head.

Final Answer: